EXTERNAL CONFIGURATION OF PL'ANTS. 191 



tiylindrical form, as in grasses, sedges, and rushes. 

 The whip-shaped yielding leaves of grasses are well 

 adapted to sustain and distribute the shock of the 

 wind. In Iris, and like forms, the two-ranked or 

 distichous arrangement of the leaves exposes a large 

 surface to the ^vind ; but the flexibility of the leaves, 

 as well as their strong tongh character, may up to 

 a certain point neutralise this disadvantage. Sir 

 John Lubbock has recently published in the Con- 

 temporary Review a most interesting article on 

 leaves. In that article he has considered the 

 arrangement of leaves in relation to light. He 

 also compai'es the weight of the foliage ^vith the 

 thickness of the branches. He is of opinion that the 

 dissection of submerged leaves does a^vay Avith the 

 necessity for an internal framework of vascular 

 tissue ; at any rate there is a total absence of fibro- 

 vascular tissue in the submerged leaves of aquatic 

 plants. Of course it is the diminished mechanical 

 resistance which makes the framework unnecessary. 

 The case of the lattice-leaf plant, Ouvirandra fene- 

 stralis, cannot be so explained. Here the parenchyma 

 of the leaf is deficient, and apparently it is the 

 skeleton only which is developed. The plant is a 

 native of Madagascar, grows in streams, and is allied 

 to our Potamogeton. Though fragile in appear- 

 ance, its leaf is by no means delicate or easily 

 injured. The i:)erf orations are probably of advantage 

 in allowing the A\'ater to pass through ; from the 

 shai^e of the leaf they can hardly be required to 

 allow gas to escape. The solution of continuity 

 observed in the large perforated leaves of Monstera 

 may possibly be of service in a similar manner. 

 The large orbicular floating leaves of water-lilies, as 

 exemplified in the well-known Victoria regia, are 

 supported by the water; and their great size would 

 lead us to infer that the weight of the leaf in the 

 majority of iilants has been an important element 

 in limiting its size. Sir John Lubbock thinks that 

 the advantage possessed by the palmate leaf is that 



